1. Field of the Invention
The present invention relates to a bed adapted to promote blood circulation of a portion of a person such as a human patient or a disabled individual, which is held in contact with a mat on the bed.
2. Discussion of the Related Art
A person confined to a bed tends to be deprived of blood at areas held in contact with a mat on the bed, due to pressure exerted on those areas by the body weight. It is known that the lumbo-sacral area and the great trochanters of a human patient easily suffer from so-called "bed sores" when the patient is confined to a bed for a long time.
In the light of the above problem, there is proposed an improved bed as disclosed in laid-open Publication No. 2-44543 (published 1990) of examined Japanese Patent Application, wherein a mat is supported selectively by two arrays of rigid parallel support beams, namely, a stationary array consisting of stationary beams and a movable array consisting of vertically movable beams. These beams of the two arrays are arranged so as to extend in the longitudinal direction of the bed such that each of the movable beams of the movable array is interposed between the adjacent stationary beams of the stationary array. The movable array is slowly moved up and down between a lower position and an upper position above and below the top plane of the stationary array, so that the mat is supported by the stationary array when the movable array is located below the top plane of the stationary array, and by the movable array when the movable array is located above the top plane of the stationary array.
In the known bed constructed as described above, each of the stationary and movable support beams is a cylindrical support member having a suitable diameter. Since the stationary and movable support beams are arranged alternately in the transverse direction of the bed, the spacing between the adjacent stationary beams or movable beams (placed in the upper position) which support the mat has to be relatively large, for example, two times the diameter of the beams. This relatively large spacing between the adjacent beams which actually support the mat undesirably results in an excessive amount of undulation of the mat, leading to deteriorated comfort with respect to the mat or bed as felt by the patient.